2. Haul Road Design
• HAUL ROADS: During the
life of the pit a haul road
must be maintained for
access.
• HAUL ROAD - SPIRAL
SYSTEM: Haul road is
arranged spirally along the
perimeter walls of the
pit.
2
3. Haul Road Design
• HAUL ROAD – SWITCH
BACK SYSTEM: Zigzag pattern
on one side of the pit.
• HAUL ROAD WIDTH: Function
of capacity of the road and the
size of the equipment. Haul road
width must be considered in the
overall pit design.
3
6. Sight Distances and Stopping
Distances
• Vertical and horizontal curves designed
considering sight distance and stopping
distance
• Sight distance is the extent of peripheral area
visible to the vehicle operator
• Sight distance must be sufficient to enable
vehicle traveling at a given speed to stop
before reaching a hazard
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7. Sight Distances and Stopping
Distances
• On vertical curves, road surface limits sight
distance
• Unsafe conditions remedied by lengthening curve
• On horizontal curves, sight distance limited by
adjacent berm dike, rock cuts, trees, etc;
• Unsafe conditions remedied by laying back bank or
removing obstacles
7
9. Stopping Distances
• Stopping distances depend on truck breaking
capabilities, road slope and vehicle velocity
• Stopping distance curves can be derived
based on SAE service break maximum
stopping distances
9
10. Stopping Distance
Characteristics
For example,
stopping
distance
characteristics
of vehicles of
200,000 to
400,000 pounds
GVW
10
11. Stopping Distances
• Prior to final road layout, manufacturers of
vehicles that will use the road should be
contacted to verify the service brake
performance capabilities
11
12. Vertical Alignment
• Establishment of grades and vertical curves that
allow adequate stopping distances on all segments
of the haul road
• Maximum sustained grades
• Reduction in grade significantly increases vehicle uphill speed
• Reduction in grade decreases cycle time, fuel consumption, stress
on mechanical components and operating costs
• Reduction in grade increases safe descent speeds, increasing
cycle time
• The benefits of low grades offset by construction costs associated
with low grades
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15. Vertical Alignment
• Maximum sustained grades
• Some states limit maximum grades to 15 to 20% and
sustained grades of 10%
• Most authorities suggest 10% as the maximum safe
sustained grade limitation
• Manufacturer studies show 8% grades result in the
lowest cycle time exclusive of construction
consideration
15
16. Vertical Alignment
• Maximum sustained grades
• Property boundaries, geology, topography, climate
must be considered on a case by case basis.
• Lower operating costs must be balanced against higher
capital costs of low grades.
• Truck simulators and mine planning studies over the
life of mine should be used to make the determination
of the appropriate grades
16
17. Vertical Curves
• Vertical curves smooth transitions from one
grade to another
• Minimum vertical curve lengths are based on
eye height, object height, and algebraic
difference in grade
17
18. Stopping Distance vs. Vertical Curve
For example,
vertical curve
controls 9 ft eye
height (usually
minimum height
for articulated
haulage trucks of
200,000 to
400,000 pound of
GVW)
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19. Horizontal Alignment
• Deals primarily with design of curves and
considers previously discussed radius, width,
and sight distance in addition to
superelevation
• Cross slopes also should be considered in the
design
19
20. Curves, Superelevation, and
Speed Limits
• Superelevation grade recommendations vary
but should be limited to 10% or less because
of traction limitations
• Depending on magnitude of the side friction
forces at low speed, different values are
suggested for small radius curves
• Kaufman and Ault suggest .04-.06 fpf
(basically the normal cross slope)
20
21. Curves, Superelevation, and
Speed Limits
• CAT suggests higher slopes with traction
cautions and 10% maximum caution
• Again, where ice, snow, and mud are a
problem, there is a practical limit on the
degree of superelevation
21
24. Curves, Superelevation, and
Speed Limits
• Centrifugal forces of vehicles on curves are
counteracted by friction between tire an road and
vehicle weight as a result of superelevation
• Theoretically, with superelevation, side friction
factors would be zero and centrifugal force is
balanced by the vehicle weight component
• To reduce tire wear, superelevation or speed limits
on curves are required
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25. Combinations of Alignments
• Avoid sharp horizontal curvature at or near the crest
of a hill
• Avoid sharp horizontal curves near the bottom of
sustained downgrades
• Avoid intersections near crest verticals and sharp
horizontal curvatures
• Intersections should be made flat as possible
• If passing allowed, grades should be constant and
long enough
25
26. Cross Section
• A stable road base is very important
• Sufficiently rigid bearing material should be
used beneath the surface
• Define the bearing capacity of the material
using the California Bearing Ratio (CBR)
26
29. Cross Slopes
• Cross slopes provide adequate drainage and
range from ¼ to ½ inch drop per foot of
width (approximately .02 to .04 foot per foot)
• Lower cross slopes used on smooth surfaces
that dissipate water quickly and when ice or
mud is a constant problem
29
30. Cross Slopes
• Higher cross slopes permit rapid drainage,
reduce puddles and saturated sub-base, and
are used on rough surfaces (gravel and
crushed rock) or where mud and snow are
not a problem
• High cross slopes can be particularly
problematic with ice or snow on high grades
(+5%)
30
32. Width
• On straight or tangent segments, width
depends on
• Vehicle width
• Number of lanes
• Recommended vehicle clearance, which ranges
from 44 to 50% of vehicle width
32
36. Width
• Berm height and width as a function of
vehicle size and material type
• Ditch(es) added to basic recommendations
• Runaway provisions may also add to width
• Road wider on curves because of overhang
• Minimum turning radius considered on
curves (should be exceeded)
36
38. Safety Provisions - Berms
• Triangular or trapezoidal made by using local
material
• Stands at natural angle of repose of construction
material
• Redirects vehicle onto roadway
• Minimum height at rolling radius of tire
38
39. Berms
• Larger boulders backed with earthen material
• Near vertical face deflects vehicle for slight
angles of incidence
• Problems with damage and injury and
availability of boulders
• Minimum height of boulder at height of tire
allowing chassis impact
39
40. Runaway Provisions
• With adverse grades some safety provision should
be integrated to prevent runaway vehicles
• Primary design consideration is required spacing
between protective provisions
• Driver must reach a safety provision before truck
traveling too fast to maneuver
• Maximum permissible speed depends on truck
design conditions and operator
40
41. Runaway Provisions
• Maximum permissible speed, equivalent
downgrade, and speed at break failure determine
distance between runaway truck safety provisions
• For example, at an equivalent downgrade of 5% and
a maximum speed of 40 mph,
Speed at Failure 10 mph 20 mph
Provision Spacing 1,000 ft 800 ft
(Kaufman and Ault)
41
43. Median Runaway-Vehicle
Provision Berms
• Vehicle straddles collision berm and rides
vehicle to stop
• Made of unconsolidated-screened fines
• Critical design aspects spacing between
berms and height of berm
• Height governed by height of undercarriage
and wheel track governed by largest vehicle
43
44. Median Runaway-Vehicle
Provision Berms
• Requires maintenance in freezing conditions
• Agitation to prevent damage to vehicle
• May cover berm in high rainfall areas
44
45. Escape Lanes
• Good tool for stopping runaway but
expensive to construct
• Entrance from road is important; spacing,
horizontal, vertical curve and superelevation
are all considered in design
• Deceleration mainly by adverse grade and
high rolling resistance material
45
46. Escape Lanes
• Length a function of grade and speed at
entrance and rolling resistance
• Stopping by level section median berm, sand
or gravel or mud pits, road bumps or manual
steering
46
48. Maintenance
• The road surface is
deformed by the constant
pounding of haulage
vehicles.
• A good road maintenance
program is necessary for
safety and economics.
48
49. Safety Considerations
• Dust, potholes, ruts, depressions, bumps, and
other conditions can impede vehicular
control.
49
50. Economic Considerations
• The wear on every component is increased when a
vehicle travels over a rough surface.
• If the vehicle brakes constantly, unnecessary lining
wear occurs as well.
50
51. Dust Control
• Dust may infiltrate brakes, air filters,
hydraulic lifts, and other components of
machinery.
• The abrasive effect of dust will result in
costly cleaning or replacement of these
items.
51
53. Motor Graders
• A motor grader
should be used to
maintain cross slopes,
remove spills, and to
fill and smooth
surface depressions as
they occur.
53
54. Road Drainage
• To avoid overflow, roadside ditches and
culverts should be periodically cleaned.
• Avoid erosion or saturation of subbase
materials.
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